Method of vulcanizing tires



March 3, 1936. F. A. SEIBERLING ET AL 9 5 METHOD OF' VULCANIZING TIR ES Filed Dec. 26, 1933 0 4 V ATToRwE g Patented Mar. 3, 1936 UNITED STATES PATENT OFFICE METHOD OF VULCANIZING TIRES Ohio Application December 26, 1933, Serial No. 703,938

6 Claims.

This invention relates in general to a method of vulcanization, but, as indicated, has reference more particularly to a method of vulcanizing automobile tires and the like.

At the present time, the curing of automobile tires is usually accomplished in metal molds, the tire being placed in the mold and expanded against the inner surface thereof by means of a thick, heavy rubber bag which is disposed within the mold and inflated by air under pressure. Dry steam at a relatively high temperature is then conducted through the passages provided in the mold and heat is thus applied to the outer surface of the tire. It is virtually impossible by this method to obtain a perfect cure of the tire for the reason that when the proper degree of vulcanization is reached in the outer P rtions of the tire, the inner portions or the cord plies and the rubber around the cords in the plies, may still be in an undercured condition. On the other hand, if, as is necessary, the application of such heat is continued until the inner portions are properly vulcanized, the outer portions in direct contact with the mold will be over-vulcanized, leading to so-called flex-cracking and other defects which materially reduce the life of the tire in service. Furthermore, owing to the difficulty of properly regulating the various factors in the mold-vulcanizing process, the vulcanization is often prolonged to such an extent as to cause overheating of the cord plies of the tire with a resultant decrease of the flexing qualities thereof.

In spite of every precaution which may be taken to insure uniform and thorough vulcanization of the tires, a tire may, to all outward appearances, appear to be perfectly cured, but no inspection can detect undercure or overcure on the inside of the tire which may later develop into a weakness, causing separation of tread or cord plies and possibly a blowout on the road.

It has also been proposed to secure a penetration of heat into the tire through the inner as well as the outer surface thereof, as by forcing hot water through the rubber bag used in the aforesaid process. While this constitutes something of an improvement, the heating effect of the water through the wall of the rubber bag is not as great as that of the steam through the wall of the metal mold, and owing to the thickness of the base of the bags usually employed for this purpose, access of heat to the beads of the tires is rendered extremely difficult, rubber being a poor conductor of heat, and as a result, the bead portions of the tires are not properly vule canized,

plies and the wear resistance of the tread of the tire, and a considerable increase in the production of tires per mold by shortening the period of use thereof per tire.

To the accomplishment of the foregoing and related ends, said invention, then, consists of the means hereinafter fully described and particularly pointed out in the claims; the annexed drawing and the following description setting forth in detail one method constituting, however, but one of various applications of the principle of our invention.

In said annexed drawing:-

Fig. 1 is a fragmentary cross-sectional view, showing the first stage of the curing of tires in accordance with the present improved process; and Fig. 2 is a view showing in a more or less diagrammatic manner the second stage in the curing of the tires.

In accordance with our improved process, the tire I which is in an uncured condition, is placed within an annular metallic mold 2, which, as shown in Fig. l, is provided in its walls with passageways 2a. An annular rubber bag 3, which is disposed within the mold, is then inflated, as by means of hot water, causing the tire to be expanded into contact with the wall of the mold. Steam is also conducted through the passageways 2a of the mold and the temperature of the steam and hot water are preferably so controlled that the heat penetrating the tire from the inside meets the heat penetrating the tire from the outside at approximately the center of the tire. The heating is continued for a period of time suflicient to set the tire, that is, solidify the rubber and cotton so that the tire may be re-' moved from the mold without distortion. This set cure is a partial vulcanization of the tire and proceeds to a point somewhat beyond the point at which the tire would blow upon removal thereof from the mold.

The blow point may be described as that point in the vulcanization of the tire at which,

due to the presence of occluded gases, such as assume a somewhat puffed or blown condition,

at least in places. This condition may be accompanied by a separation of the tread from the cord plies, and by other defects, which are not discernible upon a mere casual inspection of the tire. The blow'p'oint, or rather. the point after which the tire, upon removal from the mold, will no longer tend to assume a puffed or blown on dition, varies of course in accordance with the size and composition of the tire, the temperature used and other factors, but for any given size of tire and composition, may be empirically determined with a, fair degree of accuracy.

We have found in practice that if the tire is removed from its mold directly after the blow point has been reached, the the will exhibit no tendency to blow, but will be properly set. It w however be nly ar i r v canize but no'portions of the tire will have been over-cured. The duration of this set pure will vary with the size of the tire and the other factors men tioned'abovejbut in general, it may be stated i i rqm b it 0% to th m 5 es than the time consumed in the full vulcanizin'g treatmentsby methods heretofore employed.' In e -i W have i un t at the tire ma be a yjremq e now h mold i 'a' u to six minutes, after] the blow point is'reach'ed. By thus rducin tn time at which the cord pliesare subjected tothe relatively 'high curing temperature, mana ing qualities thereof are preserved.' Furthermore, by'reducing'the length of time during whieh eaeh' tire is in the "mold, the'pro'duction capacityofthe mold is obviously greatlyiricreased. Following,theset cure, the partially vulcanized tires are removed from the molds'and hung n s d s 4. whi' h w ifi F are movablfmounted on 'a 'rail' or track}, "extending through a cylindrical chamber"6',' provided with a door 1, adapted to bev swung outwardly when the chamber i s bein g filledwi'th tires. The tires within the chamber are then exposed to the acti n q water vane i t a t a temperature from aboiitf250 to 2 5 and preferably at a'temperat'ure of approximately 253 F. for a length of time sufiicient to complete the V111- canization oi the tires This manta of completing the vulcanization is: not only efficient in thati t, involves a direct' a plication of'heat of the same degree to allsurfaces of the tires, both ide nd out, u s a s Safe, s he t mpera: tur'ei' employed is" sufficiently 'low' to" avoid the possibility of"over curing portions ofthe tire. Moreover, the cost of the treatment is low as compared with the m'old'vulcaniz'ing treatment,

as a large number oftires, e; g'., batches of 40 or more], may be simultaneouslyheated in equipment which is relatively inexpensive as compared with the'cestof moldsfand accessory apparatus for vulcanizing a similar number of tires. Consequently, this; treatment, which we term a final cure,'may be conducted'leisurely and for a 'pe'- r'iod of time which will insure uniform vulcaniza- Of the tire; i t k t As already stated, the duration of the set and fina cures wi Vary} t'o ac ord to the size of the tire which is being vulcanized, but

also with the character of the compound oncomposition as wellas the temperatures employed. However, the temperatures and times of vulcanization of. various sizes of tires by existing,

as well as by the present improved method, set forth in the table below, may be taken as typi-- cal:

Time and tempera- Time and tem perature of Size of tire 3g; 3 255 vulcanization by improved methods methods Small 40 min. at 295 F. 32 min. at 295 F. (set cute) min. at 258 F. (final cure) Medium 90 min. at 280 F. min. at 280 F. (sat cure) -75 min. at 258 F. (final cure) Large 75 mm. at 240 F min. at 258 F. (set cure) 60 min. at 258 F 60 min. at 274 F. (set cute) 75 min. at, 27? F -90 )min. at 258 F. (final cure In the above table, the data given for the large size of tire is that for a single cure which, as indicated, is" carried out in three stages, that is to say, under existing methods, the tire is vulcanized at 240 F. for 75 minutes, then at 258 1?. for 60 minutes, and finally"at274 F. for'lti 'By the'improved method, a sihgle' cure comp'ris'e's' the set cure which is carried out in two tages; as indicated, and the final'cure at 258F. for to 0 minutes. t t, i ,o

'Asi'a'result of the present improved method, the tires are aimed uniformly "throughout, the flexing qualities of the cord 'pliesare'improve'd, the wear resistance of 'theftrea'd portions he tire materially improved, and the production of tires per mold considerably increased.

Qther modes of applying tl'ie'pfi'ficiple of our invention may be employed instead "of the" one explained, change beingmade "as regards the process herein disclosed, provided the step'or steps statedby anyo'f'the following alarms or t e equivalent of h stated ste wrstiisf be mp l g ,7 .v We therefore particularly point out and dis tinctly claim asour'inve'ntion z 1. The method of vulcanlzing tires which con: sists in initiating the vulcanization in a tirefog-m g mold, continuing the vulcanization in suchinold tea pd ntlieybn i'that atwmcmne tire would tend to "blow "if"rerrioi ed from the mold but of complete vulca'nizatidnbf the tire, removing the partially curedtire from the mold, and 'completijnig'thevulcariization by" exposing thetir to "the direct matter steam. The method of vulanizing tires'which'consists ininitia'ting the vulcanization in 'tli'tireforming molds, "deepening the meanest-ion in such molds 'ror gfsnr'priaa after the blow point reached, remo ing" the tires fronfthe molds and completing the'vul'canization by exposing the uiestgm direct action orsteam. 3IThe methodof 'vdlcarii'zing' tireswlfich 'consists iii irji tiat ifi thdvillcahi'z ationdh the tireforming fiolds,"cofitihuifig"the vulcanizationih such molds" for, sevrafmifiutes' after the blow reached, removing" the tires from the molds sndwoiripieungtne vulcanization by exposing the tires "to the directa'ction of water vapor-at 'atei'n" ratifiedfrom about 250 F. to d i V.

4."The method of vulcanizing tires which con sists iii initiating the'v'l'flca nizjatio ri in th tire forming iiiolds'fcontihuing the vulcanization 'in such'lriolds" r6: abrie'f period after the blow point reached, rmoving the tires from the molds and completing thevulcanizatiori by exposing the tiresto'the directtie on of water i l a a em er tu e 9 prq m. ,e 8 F; 5. The method of vulcanizing tires con sists in initiating the vulcanization in the tireforming molds, continuing the vulcanization in such molds until about four to six minutes after the blow point is reached, removing the tires from the molds and completing the vulcanization by exposing the tires to the direct action of water vapor.

6. The method of vulcanizing tires which consists in initiating the vulcanization in tireforming molds, continuing the vulcanization in such molds until about four to six minutes after the blow point is reached, removing the tires from the molds and completing the vulcanization by exposing the tires to the direct action of water vapor at a temperature of from about 250 F. to about 265 F.

FRANK A. SEIBERLING.

CLINTON A. CARLTON. 

